What is the issue?

• Atlantic Meridional Overturning Current (AMOC) is thought to be slowing down for the last 15 years, which could have drastic consequences on global climate.
• A new study suggests that AMOC is getting help from the Indian Ocean.

What is an AMOC?

• Atlantic Meridional Overturning Current is the large system of ocean currents operating in the Atlantic Ocean.
• It circulates the waters between the north and the south.
• It ensures the oceans are continually mixed, and heat and energy are distributed around Earth.
• Warming as a result of climate change, the Indian Ocean is causing a series of cascading effects that is providing AMOC a “jump start”.

How AMOC works?

• As warm water flows northwards in the Atlantic, it cools, while the evaporation increases its salt content.
• Low temperature and high salt content raise the density of the water, causing it to sink deep into the ocean.
• The cold, dense water deep below slowly spreads southward.
• Eventually, it gets pulled back to the surface and warms again and, the circulation is complete.
• This continual mixing of the oceans, and distribution of heat and energy around the planet, contribute to global climate.
• Another oceanic system, which is more frequent, is the El Niño-Southern Oscillation (ENSO).
• This involves temperature changes of 1°-3°C in the central and eastern tropical Pacific Ocean, over periods between 3 and 7 years.
• El Niño refers to warming of the ocean surface and La Niña to cooling, while “Neutral” is between these extremes.
• This alternating pattern affects rainfall distribution in the tropics and can have a strong influence on weather in other parts of the world.

What is happening now?

• AMOC has been stable for thousands of years.
• Data since 2004 and projections are cause for concern.
• It is not clear whether the signs of slowing in AMOC are a result of global warming or only a short-term anomaly.
• Yale University research - AMOC had weakened substantially 17,000 to 15,000 years ago.
• The new study, by Fedorov and Shineng Hu of Scripps Institution of Oceanography, appears in Nature Climate Change.

What is Indian Ocean’s role?

• Fedorov and Hu’s work involves climate mechanisms that may be shifting due to global warming.
• Using observed data and computer modelling, they have plotted out what effect such shifts might have over time.
• In this study, they looked at warming in the Indian Ocean.
• Their findings - As the Indian Ocean warms faster and faster, it generates additional precipitation.
• This draws more air from other parts of the world to the Indian Ocean, including the Atlantic.
• With so much precipitation in the Indian Ocean, there will be less precipitation in the Atlantic Ocean.
• Less precipitation will lead to higher salinity in the waters of the tropical portion of the Atlantic.
• This saltier water in the Atlantic, as it comes north via AMOC, will get cold much quicker than usual and sink faster.
• This would act as a jump start for AMOC, intensifying the circulation.
• Concern - It is not know how long this enhanced Indian Ocean warming will continue.
• If other tropical oceans’ warming, especially the Pacific, catches up with the Indian Ocean, the advantage for AMOC will stop.